All the library i /o functions (like getchar, scanf , gets etc.) use the same interme-diate buffer and share the same file pointer. So, they can be interleaved in any order to access consecutive characters in a tile without causing any inconsistency. Unlike them. system calls (like read and write) directly manipulate the tile. So, mixing system calls and library function will have undesired consequence

return statement when executed transfers control back to the calling environment. So, if a subroutine executes a return statement control comes back to the main routine. exit always terminates the program, which means within the main routine, exit and return can be used interchangeably.